Image forming apparatus and detecting method of pattern image regarding image quality adjustment

Abstract

An image forming apparatus includes: an obtaining unit that radiates light from a light-emitting unit onto the image carrier and that obtains an output value of a light-receiving unit having received the light reflected from the image carrier; a light amount setting unit that calculates a required light amount value and that sets a light amount adjusting value; a detecting unit that detects a pattern image on the image carrier and by judging whether an output value obtained by radiating light of the light amount adjusting value exceeds a predetermined threshold; and a controller that controls image formation on the image carrier based on a detected result, wherein the detecting unit reduces the threshold when the required light amount value exceeds the limiting value depending on degree of the excess.

What is claimed is: 
     
       1. An image forming apparatus that forms an image on an image carrier and transfers the image thus formed on paper to be fixed, the image forming apparatus comprising:
 an obtaining unit
 that radiates light from a light-emitting unit onto the image carrier and 
 that obtains an output value of a light-receiving unit having received the light reflected from the image carrier; 
 
 a light amount setting unit
 that calculates a required light amount value indicating a light amount required for the light-emitting unit based on the output value and 
 that sets a light amount adjusting value indicating a light amount of the light-emitting unit using a limiting value preset as an upper limit based on the required light amount value thus calculated; 
 
 a detecting unit that detects a pattern image
 by forming the pattern image to perform image quality adjustment on the image carrier and 
 by judging whether an output value obtained by radiating light of the light amount adjusting value from the light-emitting unit exceeds a predetermined threshold for performing the image quality adjustment; and 
 
 a controller that controls image formation on the image carrier based on a detected result by the detecting unit, wherein 
 the detecting unit maintains the threshold at a constant value when the required light amount value does not exceed the limiting value, and reduces the threshold when the required light amount value exceeds the limiting value depending on a degree of the excess, the limiting value being an upper limit of a driving voltage of the light-emitting unit, 
 the pattern image includes a plurality of images, having predetermined widths, varying in a plurality of colors, and which are formed at a predetermined pitch with non-color area between the plurality of images in a sub-scanning direction of the image carrier, and 
 the obtaining unit obtains respective output values corresponding to each of the plurality of colors from each of a plurality of sensors, each sensor including one of the light-emitting unit and one of the light-receiving unit. 
 
     
     
       2. The image forming apparatus according to  claim 1 , wherein
 the detecting unit calculates the threshold by adding a predetermined offset value to standard threshold×(light amount adjusting value−x intercept)/(required light amount value−x intercept), 
 where the standard threshold indicates a preset threshold, and the x intercept is the light amount adjusting value when the light amount of the light-emitting unit is zero. 
 
     
     
       3. The image forming apparatus according to  claim 1 , further comprising:
 a recorder that records
 the required light amount value calculated by the light amount setting unit and 
 the light amount adjusting value set based on the required light amount value subsequently; and 
 
 an outputting unit that outputs
 the required light amount value and 
 a light amount set value recorded in the recording unit subsequently. 
 
 
     
     
       4. The image forming apparatus according to  claim 1 , further comprising
 a judging unit that judges presence or absence of abnormal detection of the pattern image depending on a comparative result with a predetermined judgment value based on the output value that the detecting unit obtains when detecting the pattern image, wherein 
 the judging unit reduces the judgment value when the required light amount value exceeds the limiting value depending on the degree of the excess. 
 
     
     
       5. The image forming apparatus according to  claim 1 , wherein
 the detecting unit detects a color-shift detection pattern image for correcting color shift in an image in a plurality of colors by forming the color-shift detection pattern image on the image carrier, and 
 the controller controls color image formation on the image carrier based on a detected result of the color-shift detection pattern image. 
 
     
     
       6. The image forming apparatus according to  claim 1 , further comprising
 a storage unit that stores therein the output value that the detecting unit obtains by forming the pattern image to perform image quality adjustment on the image carrier, wherein 
 the light amount setting unit
 calculates the required light amount value based on the output value stored in the storage unit at a latest process and 
 sets the light amount adjusting value based on the required light amount value thus calculated. 
 
 
     
     
       7. A detecting method for detecting a pattern image to perform image quality adjustment used in an image forming apparatus that forms an image on an image carrier and transfers the image thus formed on paper to be fixed, the detecting method comprising:
 radiating light from a light-emitting unit onto the image carrier and obtaining an output value of a light-receiving unit having received the light reflected from the image carrier; 
 calculating a required light amount value indicating a light amount required for the light-emitting unit based on the output value and setting a light amount adjusting value indicating a light amount of the light-emitting unit using a limiting value preset as an upper limit based on the required light amount value thus calculated; 
 detecting a pattern image to perform image quality adjustment by forming the pattern image on the image carrier and by judging whether an output value obtained by radiating light of the light amount adjusting value from the light-emitting unit exceeds a predetermined threshold for performing the image quality adjustment; and 
 controlling image formation on the image carrier based on a detected result by the detecting unit, 
 
       wherein
 the detecting includes maintaining the threshold at a constant value when the required light amount value does not exceed the limiting value, and reducing the threshold when the required light amount value exceeds the limiting value depending on a degree of the excess the limiting value being an upper limit of a driving voltage of the light-emitting unit, 
 the pattern image includes a plurality of images, having predetermined widths, varying in a plurality of colors, and which are formed at a predetermined pitch with non-color area between the plurality of images in a sub-scanning direction of the image carrier, and 
 the obtaining includes obtaining respective output values corresponding to each of the plurality of colors from each of a plurality of sensors, each sensor including one of the light-emitting unit and one of the light-receiving unit. 
 
     
     
       8. The detecting method according to  claim 7 , wherein
 the detecting includes calculating the threshold by adding a predetermined offset value to standard threshold×(light amount adjusting value−x intercept)/(required light amount value−x intercept), 
 where the standard threshold indicates a preset threshold, and the x intercept is the light amount adjusting value when the light amount of the light-emitting unit is zero. 
 
     
     
       9. The detecting method according to  claim 7 , further comprising:
 recording in a recording unit
 the required light amount value calculated by the light amount setting unit and 
 the light amount adjusting value set based on the required light amount value subsequently; and 
 
 outputting
 the required light amount value and 
 a light amount set value recorded in the recording unit subsequently. 
 
 
     
     
       10. The detecting method according to  claim 7 , further comprising
 judging presence or absence of abnormal detection of the pattern image depending on a comparative result with a predetermined judgment value based on the output value that the detecting unit obtains when detecting the pattern image, wherein 
 the judging includes reducing the judgment value when the required light amount value exceeds the limiting value depending on the degree of the excess. 
 
     
     
       11. The detecting method according to  claim 7 , wherein
 the detecting includes detecting a color-shift detection pattern image for correcting color shift in an image in a plurality of colors by forming the color-shift detection pattern image on the image carrier, and 
 the controlling includes controlling color image formation on the image carrier based on a detected result of the color-shift detection pattern image. 
 
     
     
       12. The detecting method according to  claim 7 , further comprising
 storing in a storage unit the output value that the detecting unit obtains by forming the pattern image to perform image quality adjustment on the image carrier, wherein 
 the light amount setting includes
 calculating the required light amount value based on the output value stored in the storage unit at a latest process and 
 setting the light amount adjusting value based on the required light amount value thus calculated. 
 
 
     
     
       13. An image forming apparatus that forms an image on an image carrier and transfers the image thus formed on paper to be fixed, the image forming apparatus comprising:
 means for obtaining an output value of a light-receiving unit
 that radiates light from a light-emitting unit onto the image carrier and 
 that obtains the output value of a light-receiving unit having received the light reflected from the image carrier; 
 
 means for setting a light amount adjusting value
 that calculates a required light amount value indicating a light amount required for the light-emitting unit based on the output value and 
 that sets a light amount adjusting value indicating a light amount of the light-emitting unit using a limiting value preset as an upper limit based on the required light amount value thus calculated; 
 
 means for detecting a pattern image
 by forming the pattern image to perform image quality adjustment on the image carrier and 
 by judging whether an output value obtained by radiating light of the light amount adjusting value from the light-emitting unit exceeds a predetermined threshold for performing the image quality adjustment; and 
 
 means for controlling image formation on the image carrier based on a detected result by the means for detecting, wherein 
 the means for detecting maintains the threshold at a constant value when the required light amount value does not exceed the limiting value, and reduces the threshold when the required light amount value exceeds the limiting value depending on a degree of the excess, the limiting value being an upper limit of a driving voltage of the light-emitting unit, 
 the pattern image includes a plurality of images, having predetermined widths, varying in a plurality of colors, and which are formed at a predetermined pitch with non-color area between the plurality of images in a sub-scanning direction of the image carrier, and 
 the means for obtaining obtains respective output values corresponding to each of the plurality of colors from each of a plurality of sensors, each sensor including one of the light-emitting unit and one of the light-receiving unit. 
 
     
     
       14. The image forming apparatus according to  claim 13 , wherein
 the means for detecting calculates the threshold by adding a predetermined offset value to standard threshold×(light amount adjusting value-x intercept)/(required light amount value−x intercept), 
 where the standard threshold indicates a preset threshold, and the x intercept is the light amount adjusting value when the light amount of the light-emitting unit is zero. 
 
     
     
       15. The image forming apparatus according to  claim 13 , further comprising:
 means for recording therein
 the required light amount value calculated by the light amount setting unit and 
 the light amount adjusting value set based on the required light amount value subsequently; and 
 
 means for outputting that outputs
 the required light amount value and 
 a light amount set value recorded in the means for recording subsequently. 
 
 
     
     
       16. The image forming apparatus according to  claim 13 , further comprising
 means for judging that judges presence or absence of abnormal detection of the pattern image depending on a comparative result with a predetermined judgment value based on the output value that the means for detecting obtains when detecting the pattern image, wherein 
 the means for judging reduces the judgment value when the required light amount value exceeds the limiting value depending on the degree of the excess. 
 
     
     
       17. The image forming apparatus  claim 13 , wherein
 the means for detecting detects a color-shift detection pattern image for correcting color shift in an image in a plurality of colors by forming the color-shift detection pattern image on the image carrier, and 
 the means for controlling controls color image formation on the image carrier based on a detected result of the color-shift detection pattern image. 
 
     
     
       18. The image forming apparatus  claim 13 , further comprising
 means for storing that stores therein the output value that the detecting unit obtains by forming the pattern image to perform image quality adjustment on the image carrier, wherein 
 the means for setting
 calculates the required light amount value based on the output value stored in the means for storing at a latest process and 
 sets the light amount adjusting value based on the required light amount value thus calculated. 
 
 
     
     
       19. The image forming apparatus according to  claim 1 , wherein
 the detecting unit detects the pattern image by forming the pattern image to include a plurality of images that vary in color in a conveying direction of the image carrier. 
 
     
     
       20. The image forming apparatus according to  claim 1 , further comprising
 the plurality of sensors, the sensors being arranged equidistantly across a main scanning direction of the image carrier.